The present invention relates to a sheet feeding device incorporated in an image forming apparatus such as a printer, a facsimile machine, and a copying machine.
Japanese Patent Publication No. 6-9079A discloses a sheet feeding device that comprises: a sheet feeding roller having a semicircular cross section; a cassette body for accommodating, in a stacked state, sheet media to be fed by the sheet feeding roller; and a pair of separating claws that are provided in the cassette body and arranged such as to cover, from the above, leading edge corner parts of the stacked sheet media relative to a sheet feeding direction, thereby separating the sheet media into each sheet to be fed by the sheet feeding roller. The cassette body is withdrawably inserted into the device main body in the same direction as the sheet feeding direction.
A sheet feeding device employing such a sheet feeding roller is constructed such as to stop at the time of operation stop (at the time of non-feeding) in such a manner that the flat portion of the semicircular cross section opposes the sheet medium in the cassette body. Normally, insertion and withdrawal operation for the cassette body is performed in this state.
Nevertheless, by any reason (for example, when paper jam occurs, or when the power is deactivated by a user during the feeding operation), an abnormal state can arise that the sheet feeding roller stops in a state that an arcuate portion of the semicircular cross section faces the sheet medium in the cassette body. Under this abnormal condition, the user withdraws and inserts the cassette body in some cases.
In the above configuration that the cassette body is inserted in the same direction as the sheet feeding direction of the sheet medium, even when the cassette body has been withdrawn or inserted by the user at the time of abnormity described above, the separating claws provided in the cassette body have been prevented from colliding with the sheet feeding roller.
Nevertheless, in a sheet feeding device, in some cases, the cassette body is desired to be constructed such that the cassette body is withdrawably inserted into the device main body in a direction perpendicular to the sheet feeding direction of the sheet medium. In this configuration, when the cassette body is withdrawn or inserted by the user at the time of abnormity described above, the separating claw located in the back part relative to the insertion and withdrawal direction of the cassette body would collide with the semicircular sheet feeding roller, so that deformation or damage would arise in the separating claw. As a result, appropriate separation operation for the sheet media cannot be performed.
The back face of the cassette body relative to the insertion and withdrawal direction thereof is made flat as disclosed in Japanese Patent Publication No. 6-329270A.
Even when a sheet medium remains in the device main body (simply referred to as a main body, hereinafter in some cases) at the time of cassette withdrawal by any reason, a user would be unaware of the situation in some cases, and hence insert the cassette body again so as to use the sheet feeding device.
In such a case, the sheet medium that remains in the main body (referred to as a remained sheet medium, hereinafter in some cases) may stay in a state pinched and squashed between the cassette back face and a face of the main body opposite to the cassette back face. This causes a problem that a part of the remained sheet medium comes in contact with a sheet medium fed from the cassette, thereby causes resistance to the fed sheet medium, and thereby prevents the fed sheet medium from being transported appropriately, so that feeding failure or skew feeding arises.
There is known a feeding device in which plural stages of cassette bodies are provided. Between these cassette bodies and the device main body, a locking mechanism is provided for locking into a mounted state when the cassette bodies are mounted on the device main body.
In the above sheet feeding device, the locking mechanism between the cassette body and the device main body has the same configuration for every stage.
On the other hand, in a sheet feeding device comprising plural stages of cassette bodies, when a user withdraws (pulls out) a cassette body, in general, withdrawal angles for the plural stages of cassette bodies differ from each other for these stages. In general, a cassette body is withdrawn in such a manner that the handle of the cassette body is somewhat lifted up. This causes a difference between the withdrawal angle for the cassette body of lower stage and the withdrawal angle for the cassette body of upper stage.
Thus, when the locking mechanism has the same configuration for every stage as described the above, the user feels a difference between the withdrawal force at the time of withdrawing the cassette body of lower stage and the withdrawal force at the time of withdrawing the cassette body of upper stage, and hence acquires a feeling that something is wrong.